The number of solid cancers and lymphoid or blood cancers is stagnant and/or rises and chemotherapic treatments provide disappointing or very insufficient results. The major difficulty comes from the fact that chemotherapeutic agents are toxic and sometimes lethal. They inhibit the proliferation not only of malignant cells but also that of normal cells which makes it necessary to find selective agents, capable of acting by themselves or in combination, in order that the inhibiting erect toward undesirable cells predominates. Having at disposition agents that are highly selective so that side effects are held to the minimum is an important objective of cancer research.
The same problem of poor selectivity and undesirable side effects occurs in the application of radiotherapy.
Considerable efforts are also given to find chemical entities that would be active against viruses that cause diseases in humans, animals and plants. The known antiviral entities also are not sufficiently selective; in addition their number is much smaller than those known to be active against bacteria and fungi.
In the case of both malignancies and viruses, it would be desirable to find entities that are active and selective at the level of abnormal cells, e.g. that will usefully affect DNA or enzymes implicated in the proliferation of malignant or virus infected cells.